This experimental investigation will extend our present studies to include a characterization of the enzyme glutamate dehydrogenase isolated from brains of young rats and brains of old rats. This characterization will permit a determination as to whether ageing in rat result in alterations of this enzyme. The specific activity, heat stability, net change, terminal amino acid groups, and tryptic peptide mapping of the enzyme isolated from rats of the two aged groups will be compared. The specific activity of the enzyme will be determined both on the basis of enzyme activity per mg of protein and per unit of antiserum. Antibodies against the enzyme will be prepared by immunizing rabbits. A more detailed kinetics analysis will also be performed on enzyme isolated from rats of each age group. This analysis will include a determination of Michaelis constants for the substrates and coenzymes for the enzyme, an examination of the relationship of enzymic activity with pH, mapping of the active site utilizing competitive inhibitors and alternate substrates, and an examination of allosteric effectors in enzymic activity. This kind of detailed kinetic analysis will provide a valuable tool in assessing conformational differences in enzyme which is hypothesized for enzyme molecules of aged organisms and will give insight into possible differences in regulatory patterns.